Many portable and mobile electronic devices, such as cell phones, personal digital assistants (PDAs), digital cameras, and the like use rechargeable batteries, such as lithium-ion battery systems, that act as a power supply that supply electronic power to these portable and mobile electronic devices. Since lithium-ion and similar battery systems are generally regarded as being somewhat less durable than nickel metal hydride or nickel-cadmium designs, there are some risks with charging and discharging lithium-ion and similar battery systems must be managed. For example, such battery systems can suffer thermal runaway and even cell rupture if being over-charged. Furthermore, over-discharge can reduce the number of charge/discharge cycles within a service life and damage the battery systems.
To reduce these risks, a protection circuit, between the lithium-ion or similar battery and a main part of device, such as a charger or a mobile electronic device, can be provided to a control conditions experienced by the battery system. Theoretically, the protection circuit discontinue the delivery of charge to or draw of charge from the battery system when an overcharge or over-discharge situation is detected. By discontinuing operation of the battery system, the protection circuit is designed to prevent the battery system from being overcharged, where the battery is charged to have a voltage above a charge threshold voltage, and being over-discharged, where the battery is discharged to have a voltage below a discharge threshold voltage.
However, in the charge/discharge protection circuit, some circuit elements for detection of overcharge or over-discharge conditions of the battery, such as MOS transistors, are generally connected directly to the charger components. When an improper charger supplies an excessively large voltage to the battery through the protection circuit, these circuit elements in the protection circuit are subjected to a high electric potential, which may cause damage to these elements of the protection circuit. In such cases, the threshold voltage of the circuit elements used for detecting battery overcharge or over-discharge conditions may be significantly varied. As a result, the characteristics and functions of the circuit elements and the charge/discharge protection circuit may be significantly varied. Using high-voltage resistant circuit elements is one solution provided in prior art to resolve the above-mentioned problem by providing circuit elements that are capable of experiencing high voltages without incurring damage. However, the use of these components comes at the cost of additional chip area and increased manufacturing cost, both costs of which are often considered highly undesirable by consumers looking for highly portable charging devices at commodity prices.
Therefore, it would be desirable to have a system and method for operating a battery charging system having the advantages provided by battery systems such as lithium-ion battery systems without experiencing the drawbacks of being susceptible to damage from over charging or discharging or incurring the manufacturing and/or additional component size costs of traditional protection circuits.